[ntp:questions] Does NTP cause an abrupt/sudden change in an orphan's system time?

unruh unruh at invalid.ca
Wed Aug 8 15:54:27 UTC 2012

On 2012-08-08, Arpith Nayak <arpithnayak at gmail.com> wrote:
> I have a server that is in the orphan mode i.e. it was not connected to the
> internet (and thus the various public NTP servers) when I booted it up. Now
> if I install ntpd oin this server and run it, will the first instance of
> ntpd cause a sudden change in the system time as well as timestamps or does
> NTP cause a slow gradual change so that it syncs up with the public server
> over a period of time?

If the time is out by less than 128msec the procedure will be gradual. If it
is out by more, ( but less than some 10s of seconds) it will
suddenly jump. If it is out by even more, ntpd will shut down completely
(unless you started it with the -g flag and this is the first jump). 
If you want more continuous behaviour, use chrony.

ntpd makes a great to-do about continuity, but jumps ifthe time is out by
more than 128ms at any time. That part of ntpd is an incoherent mess. 
(Note that it never slews by more than 500PPM either, unless it jumps (
infinite PPM). Linux at least has the ability to slew the clock by up to
100000PPM (.1 sec/sec) but ntpd does not make use of it. )

> Regards,
> Arpith

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